The invention generally relates to a compensation scheme for correcting signal distortion of the M-code signal for global positioning systems (GPS).
The global positioning system (GPS) Military Signal Design Team (GMSDT), led by the GPS Joint Program Office (JPO), has produced a recommended design of the new military signal for the L1 and L2 bands. The result is an M-code signal design, which is to be implemented in modernized satellites and in a new generation of receivers.
The motivations for GPS Modernization, as an essential part of GPS navigation warfare (NAVWAR), have been recognized. The objectives of the modernized military signal in the context of NAVWAR are protecting military use of GPS by the US and its allies, preventing hostile use of GPS, while preserving the peaceful use of the civil radionavigation service. Furthermore, Modernization entails improving performance of GPS service for both civilian and military users, while recognizing that the threat against the military user may continue to increase. Thus, the modernization objective was to design a signal that provides functions, performance, and flexibility for an enhanced military radionavigation service, while ensuring that current military and civilian receivers continue to operate with the same or better performance as they do today.
The M-code signal design provides better jamming resistance than the Y-code signal, primarily through enabling transmission at much higher power without interference with C/A-code or Y-code receivers. The M-code signal also will be compatible with prevention jamming against enemy use of GPS. The design will provide more robust signal acquisition than is achieved in conventional GPS, while offering better security in terms of exclusivity, authentication, and confidentiality, along with streamlined key distribution. In other aspects, the M-code signal will provide at least comparable performance to the Y-code signal, and preferable better performance. It also should provide more flexibility than the Y-code signal offers.
While providing these benefits, the M-code signal must coexist with current signals on L1 and L2, not interfering with current or future civilian or military user equipment. Further, it will be simple and low-risk to implement both on space vehicles and in future user equipment. In particular, since transmit power on the spacecraft is both limited and in high demand for many applications, the M-code signal design and the overall signal architecture will be as power efficient as possible.
The modulation of the M-code signal is a binary offset carrier (BOC) signal with subcarrier frequency 10.23 MHz and spreading code rate of 5.115 M spreading bits per second denoted a BOC(10.23,5.115) (abbreviated as BOC(10,5)) modulation. Spreading and data modulations employ biphase modulation, so that the signal occupies one phase quadrature channel of the carrier. The spreading code is a pseudorandom bit stream from a signal protection algorithm, having no apparent structure or period.
The baseline acquisition approach uses direct acquisition of the M-code navigation signal, obtaining processing gain through the use of large correlator circuits in the user equipment.
As enabled by the satellite's RF and antenna designs, a given satellite may transmit two different M-code signals, at each carrier frequency (but physically different carriers). This allows for a lower power signal with wide enough angular coverage for earth and space users (termed the earth coverage signal), in conjunction with a higher power signal transmitted in a spot beam (the spot signal) for greater antijam (AJ) from space in a localized region. These two M code signals, while transmitted from the same satellite at the same carrier frequency, are distinct signals with different carriers, spreading codes, data messages, and other aspects.
Because of the unique characteristics of BOC signals, there is a need for compensating for the phase difference between the upper and lower sidebands due to distortion effects.
The techniques herein below extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the above-mentioned needs.